The present invention relates to a support plate for heat exchangers, more specifically for tube heat exchangers with vertical tubes of considerable length, whose weight in combination with high temperatures expose the support plate to considerable stress. In particular, the support plate is useful in tube heat exchangers for the production of carbon black.
Carbon black is the name used for finely divided forms of carbon which are produced by incomplete combustion or thermal decomposition of natural gas or mineral oil. Depending on the method of production, different types of carbon black arise, viz. so called channel black, furnace black and thermal black (also called pyrolysis black). Furnace black is clearly the most important type of carbon black and it is used to a considerably larger extent than the other two. Also the present invention is related to specifically this type of carbon black, which in the present application is simply called xe2x80x9ccarbon blackxe2x80x9d.
FIG. 1A illustrates a conventional plant for the production of carbon black (i.e., of the type furnace black). Incoming combustion air flows through a tube conduit 1 into the upper part of a tube heat exchanger 2, in which it is preheated before the consecutive combustion of oil in the burner 9 and the combustion reactor 3. The thus preheated air is led into the combustion chamber via a conduit 5. Oil is added to said reactor via a tube conduit 4. The amount of air corresponds to about 50% of the stoichiometric amount of oxygen for a complete combustion of the oil, carbon black thereby being created. Possibly, water is also added to the reactor, which has an impact on the quality of the final product. The mixture of suspended carbon black in consumed combustion air is led away from the top of the heat exchanger via a conduit 6, through a normally water-cooled cooler 7 to a filter plant 8, normally provided with textile trapping filters. In this filter plant, the carbon black is filtered off from the gas stream, which is then led out via a nonreturn valve 16 for further purification in a plant 11, before it is let out into the free air through a chimney 12.
The construction of the conventional heat exchanger 1B may be seen more clearly in FIG. 2. The heat exchanger is of a tube type and comprises a plurality of substantially vertical tubes 13. Inside these tubes rise the hot gasses from the combustion, whereby they are cooled by the air that enters via the inlet 1 and passes outside the tubes 13 downwardly towards the outlet 5, enclosed by the shell 14. In order to increase the heat transfer, the air entering through the inlet 1 is given a reciprocating motion by arranging a plurality of substantially horizontal baffles 15. These consist of metal sheets that extend to about xc2xe of the diameter of the heat exchanger chamber, each baffle plate being provided with a number of apertures for accomodating the tubes 13. The temperature at the inlets of the heat exchanger tubes 13 may be about 1000xc2x0 C. and the air that flows into the inlet 1 may be heated to about 800xc2x0 C. These conditions involve an extremely severe stress for the materials in the heat exchanger. The part of the heat exchanger that is exposed to the highest mechanical stress is the lower part of the shell and the support plate, where the metal temperature may amount to about 900xc2x0 C. Thus, at an internal pressure of about 1 bar at said temperature, a shell diameter of about 2000 mm, a number of tubes of between 50 and about 150, and a tower height of about 13 m, it is easily understood that the support plate must endure extremely large stresses, particularly in view of the fact that the tubes 13 rest with their whole weights upon the support plate. The corresponding problem for the shell 14 has been solved by our previous Swedish patent application 9504344-4, which is hereby incorporated by this reference. According to said patent application, the heat exchanger comprises a further shell wall, which is substantially cylindrical and placed inside and substantially concentrically with the outer shell wall, so that a substantially cylindrical gap space, that is open at both ends, is formed between the two shell walls, the gas flowing into the inlet passing this gap space before it comes into contact with the heat exchanger tubes. It has sometimes occurred that the support plate has yielded to the large load, with very high repairing costs as a consequence.
Attempts have been made to cool the support plate by means of double bottom constructions in accordance with FIG. 2. According to this construction, a portion of the air entering the inlet 1 is passed off into a stand tube 17 and down into the double support plate 18, which comprises an upper heat-insulated wall 19 and a lower heat-insulated wall 20, so that a cavity 21 is formed therebetween. The air from the stand tube 17 flows into the cavity 21, whereby it cools the support plate, and then the air flows out through the outlet tubes 22 and is returned to the heat exchanger. However, this construction has not turned out to be sufficiently efficient, since it does not cool the support plate sufficiently.
Thus, the object of the present invention is to provide a support plate in a tube heat exchanger, which plate withstands the large load and the high stress that such a plate is forced to sustain.
This and other objects have been attained in a surprising way by providing a support plate that comprises an upper spar support plate, a lower spar support plate, and a spar space formed between those plates. Heat exchanger tubes extend through the support plate. Inlets and outlets are connected to the spar space for conducting a cooling medium therethrough. The spar space is divided into a plurality of adjacent canals by partition walls. Each canal is provided with one of the inlets and one of the outlets and is intersected by a plurality of the heat exchanger tubes which pass through the spar space.
The invention also pertains to a tube heat exchanger for the production of carbon black, the heat exchanger employing the above-described support plate.